Watch this horror video of me trying to quiet mine.
You can stop or mute this video if it's annoying, but you cannot stop an actual Nest protect.
This went off in my house all day, annoying my neighbors.
When I got the Android notification that my house was burning down I immediately assumed it was false, since my Nests had already cried wolf before. I also checked video cameras and saw my house wasn't actually burning down, so I stayed at work. My poor neighbors, though.
Disclaimer: I am a Google employee. I paid for these myself. So I speak as myself.